Discuss the difference and connection between SDH, MSTP, OTN and PTN

SDH Synchronous Digital Hierarchy

MSTP Multi-Service Transfer Platform based on SDH

OTN Optical Transport Network

PTN Packet Transport Network

ASON Automatically Switched Optical Network Automatically Switched Optical Network

WSON Wavelength Switched Optical Network based on WDM

SDH-MSTP

The first thing to talk about is the concept of TDM. TDM is time division multiplexing, which is to divide a standard duration (1 second) into several small time segments (8000), and each small time segment (1/8000=125us) transmits one signal . The circuit scheduling of the SDH system is based on TDM. Therefore, many people say that the SDH service is the TDM service, which is the traditional circuit scheduling. This is based on theory.

However, when SDH was very popular, in another battle between Ethernet and ATM (asynchronous transmission, not a cash machine), Ethernet won an overall victory, so Ethernet became popular, and IP was the most powerful, resulting in Today, many business sides are IP-based, and it cannot be said that Ethernet is too good.

Question: SDH is one of the biggest influencers, and Ethernet is another big influencer. Can they work together?

Result: The two hit it off, and MSTP was born!

However, the equity distribution in the MSTP joint venture is very uneven: SDH holds 70%, Ethernet holds 20%, and ATM holds 10%. The power is still SDH, the kernel is still TDM, and all the disadvantages of TDM still exist, such as rigid pipes. Ethernet and ATM have not come up with anything decent because of the issue of equity, but they must have their own tables (provide corresponding interfaces).

With the vigorous popularization of the Internet, computers, mobile phones, TVs and other terminals can be connected to the Internet, and the demand for bandwidth has increased sharply. The opportunity for telecom operators to make money has come, but the challenge has also come. In the past, 1*155M can be used for thousands of people. Making phone calls, people still need to surf the Internet when making phone calls, and there is a contradiction between the increase in bandwidth demand and the resources of the existing network.

How to resolve this contradiction?

First, let’s take a look at how SDH, the popular man, usually gets along with people (Ethernet, ATM):

The celebrity SDH has always gone his own way and never shared public resources with others. For example, the second ring road (an optical fiber) was approved for me to run, and other vehicles were not allowed to pass by the second ring road, and I was the only one on it. At the beginning, my car could pull 1 guest (1 STM-1), so the efficiency of the second ring was (155M). Later, the tonnage of the car was upgraded, and I could pull 64 guests (64 STM-1), then the two The efficiency of the ring is (10G), which is the SDH ring rate, and the current maximum is 40G.

In this way, if there is a period of time when no one needs to be transported, then I will run empty and look at the beautiful scenery along the way. At this time, my efficiency is 0, and it has nothing to do with me even if other roads are blocked.

Due to being stubborn, there are many frustrations. For example, my car can hold 64 guests, but now there are 65 guests. Sorry, I can only hold 64 people. This inefficient operation method is called rigid piping.

Now there are more and more customers (data) that need to be transported, and they are too busy. There are three solutions:

The first: repair a few more roads (new optical cables), and divert personnel; disadvantages: the cost and cycle are too long

The second: upgrade the tonnage of the car (increase the speed); Disadvantages: have not developed a vehicle with a larger load (limited electronic components)

The third: Divide the second ring (optical fiber) into multiple lanes (wave channels), and multiple vehicles share the road. After the leader sees it, he immediately instructs: Plan 3 is feasible, and execute it immediately! In this way, the wave division is generated.

WDM

Wavelength division WDM is to put vehicles (signals) in multiple lanes (wave channels) on the same road (optical fiber) for transmission. Here, it is divided into two categories according to the size of the lane spacing: the lane spacing is 20nm, which is sparse wavelength division. , also known as Coarse Wavelength Division (CWDM); if the lane interval is 0.2nm-1.2nm, it is Dense Wavelength Division (DWDM).

In this way, the bandwidth is doubled, temporarily solving the problem of insufficient bandwidth. After WDM has been reused, it has been adopted in various places. Now WDM (Metro Wave Division) is used not only in urban trunk roads, but also on inter-city and inter-provincial roads.

The way it works is that various types of goods or passengers (business signals) are loaded into one car, the car travels in a pre-assigned lane (wave channel), and the middle car needs to be refueled. We also set up gas stations (light OLA), the drivers and passengers need to eat and rest to replenish their physical strength, we set up a temporary rest area for them (relay station – compensation for light attenuation, dispersion in long-distance transmission, elimination of signal deformation, noise, etc.), of course, we still can’t do without the traffic police System support (optical monitoring OSC or electrical monitoring ESC).

With the continuous increase in demand, the number of lanes (channels) has also expanded from 16 or 32 at the beginning to 40, 80, and 160. The current construction level (manufacturing process) has exceeded 200 lanes (channels), but Our management level is very low, mainly reflected in the following aspects:

1. Poor transmission of traffic management information (lack of OAM): The original intention of WDM is to solve the problem of insufficient bandwidth, and it does not take into account the management problem after the bandwidth is increased. The biggest problem now is that there are too many vehicles, and the traffic police (OSC) feel powerless about how to know the status of each vehicle. At this time, several SDH drivers and passengers whispered: Our SDH system has a unified management organization, and each car has drivers and conductors (SOH segment overhead, POH channel overhead, AU PTR management unit pointer), division of labor Clearly, there is also real-time video surveillance (online monitoring), the company can understand the real-time operating status of each vehicle, and the management of WDM is too bad.
2. The scheduling is not flexible enough: WDM has a serious defect at the beginning of its design. For example, when a cargo is transported from Xi’an to Beijing, the pre-allocated lane is 10 lanes (the 10th wave), then the whole journey from Xi’an to Beijing is the 10th lane. , cannot be changed, unless you have passed through several high-speed sections (optical regeneration sections), such as Xi’an-Zhengzhou-Beijing, then there is an opportunity to change lanes in Zhengzhou, and the price of this lane change is to build a special lane for this behavior. Trail (layout fiber). In the past, when SDH encountered a similar situation, it built a large dispatch center in Zhengzhou, and all the problems were solved.
3. Easy to block (imperfect protection): On urban main roads or inter-provincial expressways, in order to improve efficiency, the difference from ordinary roads is considered in the design of highways, and only a few exits are set up, and other places It is completely closed, and the consequence of this is that in the event of congestion or traffic accidents, passengers will be in a commotion (business interruption). In the SDH system, as soon as the driver sees the traffic jam in front, he immediately takes a side road and runs away. There may be a few passengers who cannot get off the bus at the destination (a small amount of business interruption), but most of the passengers can reach the destination smoothly. There are plenty of detours available, plus flexible scheduling (it’s up to the driver).

The Bureau of Transport (ITU-T) saw the problem and made reforms in the following areas:

1. Add monitoring equipment and necessary security administrators to all vehicles on the road – increase OAM overhead
2. Add a dispatching hub at the transportation hub node – increase business dispatching, which is divided into inter-lane dispatching (optical layer dispatching) and cargo or passenger dispatching (electrical layer dispatching)
3. Relying on the dispatching hub, reserve some lanes or some vehicles on the road to provide perfect protection for all vehicles – perfect protection mechanism

SDH said: What kind of reform is this, we have always done this, but the capacity is not as big as yours.

WDM responded: My capacity is indeed larger than yours, but I am not as good as you in management.

SDH and WDM decided to cooperate, and the two complemented each other’s advantages, so OTN was born.

OTN

OTN integrates some advantages of SDH on the basis of WDM, such as rich OAM overhead, flexible service scheduling, and perfect protection methods.

The scheduling of OTN services is divided into: optical layer scheduling and electrical layer scheduling. Optical layer scheduling can be understood as the category of WDM, and electrical layer scheduling can be understood as the category of SDH. So simply put: OTN=WDM+SDH. However, the electrical layer scheduling of OTN is somewhat different from that of SDH.

Review the characteristics of SDH:

Unified departure frequency, 8,000 departures per second, and the system regulations cannot be changed (following the PDH system).

The capacity is increased by developing larger tonnage vehicles. High-capacity vehicles are generally made up of 4 vehicles with a lower capacity level, so the structure of vehicles with different capacities is different.

OTN electrical layer scheduling features:

All vehicles are uniform in size, specification and capacity;

Increase the frequency of departures according to demand;

advantage:

There is no need to continuously develop larger-capacity vehicles, reducing development costs;

Unified structure, easy to manage;

Convenient cross-regional transportation (convenient communication between different manufacturers);

In theory, the capacity can be infinitely increased by increasing the frequency of departure, and the implementation method is simple and clear;

The current SDH is only equivalent to a hall owner under the head of OTN, so how is the development of the other popular Ethernet?

It is said that Ethernet and ATM were like the Huashan School in those days, they mastered the martial arts with exquisite swordsmanship, and had a high prestige in the martial arts. However, in the Huashan School, it is divided into Jianzong, which is mainly based on swords and supplemented by Qi, and Qizong, which is mainly based on Qi and supplemented by swords. Ethernet is like Jianzong, and ATM is like Qizong.

Ethernet is known for its simplicity, and it attracts many disciples because of its ease of use; ATM, because of its profound inner strength, has few practitioners. It is puzzling that the ethereum wins the final battle, which does not match the plot of the novel.

Ethernet is troubled by how to carry forward this sect, and ATM is also depressed for having such a profound martial arts but no one appreciates it. ATM wanted to borrow Ethernet to increase its influence, and Ethernet wanted to borrow ATM to increase its momentum. The two former rivals hit it off. After months of secret discussions and a year later, the two jointly released a new martial arts book. Tips MPLS (Multi-Protocol Label Switching). This martial arts secret was later adapted into several versions, and it is an important foundation for other martial arts.

Core comparison:

The momentum of Ethernet is getting bigger and bigger, and now there is MPLS to help out, and gradually has the strength to compete with SDH, so there is the initial integration of SDH and Ethernet – MSTP. But MSTP is still the protagonist of SDH because of the issue of equity, and Ethernet and ATM can only be supporting roles, so Ethernet is not happy, and he wants to find a new way out.

In order to fight against SDH, Ethernet vigorously develops its own sphere of influence, taking the route of encircling cities from rural areas, and first IP-based terminal (service-side IP-based). IP can be used as SDH cargo and transmitted through SDH, but the problem immediately arises: SDH has strict shape requirements for cargo at the beginning of its development, it must be a “block structure”, and the size is also standard, and each seat is also in accordance with This requirement is done so that the transportation efficiency is the highest. Later, there were more and more peculiar-looking (different formats) goods such as IP. Even if MSTP was specially developed (MSTP just reserved a few special seats for IP and ATM on SDH vehicles), IP still could not be well received. transportation. The reason is that IP is a proud disciple of Ethernet, and Ethernet is based on the characteristics of simplicity, unrestrainedness, and best effort. Therefore, IP also has this characteristic, some small, some fat (IP frame). variable length). If there are fewer IPs in SDH/MSTP, the problem is not big; if the IP accounts for more than half, then the cost of retrofitting the vehicle is too great.

[MSTP: If the packet service is less than 50%, there is still a cost advantage]

The problem now is that there are more and more IP cargoes. Ethernet wants to set up its own transportation company, and it has to decide by itself, and does not want to be subject to SDH anymore; at the same time, SDH is also thinking about whether it can divide the carriage into two layers and one layer. For the original business, one layer is reserved exclusively for IP, so that both can be taken into account.

MSTP+ (Hybrid MSTP)

Let’s talk about the SDH camp first. Due to the uneven distribution of equity when MSTP was established, there are many remaining problems, which makes Ethernet very dissatisfied. Now SDH Group has launched MSTP+ (also called Hybrid MSTP) after research, 50/50 equity distribution, vehicle change It is divided into two layers, the two layers are managed and scheduled separately, and two sets of scheduling systems (dual-kernel crossover) are also a good compensation measure.

IP-RAN and PTN

As for the Ethernet camp, because we are used to being free and loose, there are now two differences: one thinks that the transportation company we set up cannot let SDH customers (TDM business) get on the train. Simulation), at the same time we have no time guarantee (no time synchronization), we purely serve Ethernet, our transport company is called IP-RAN (IP Radio Access Network, compared to the traditional SDH transport network, IP RAN is based on IP transmission network).

A kind of customers who think that we should absorb some SDH customers. After all, SDH has been in business for so many years, and its customers are still many (and there are many TDM business needs), but when it comes in, it has to change its appearance – camouflage (simulation), and then it can be used in our Activity in the gang, after going out, remove the disguise and restore to the original appearance. Our transportation company is called PTN. Either way, disguise – disguise is indispensable, and then PWE3 disguise was developed.

There are two major factions in the PTN company: one is the MPLS-TP faction that combines MPLS, PWE3 and MSTP; the other is the PBT faction that combines QinQ and MSTP. For MPLS-TP supporters, there are many heavyweight stars such as Huawei, ZTE, Fiberhome, Alan, Ericsson; for PBT supporters, only Nortel Networks is the only one. So now most of the PTNs we see are MPLS-TP.

As they learn from each other, the difference between IP-RAN and PTN is getting smaller and smaller. The advantage of IP-RAN is the three-layer connectionless service, but PTN can also be implemented now; PTN used to transmit TDM services of SDH. , specially developed a clock synchronization system called 1588 system, now using the V2 version, the V3 version is being tested, and now IP-RAN also supports this system.

MSTP+ (Hybrid MSTP) can be seen as a compromise solution from SDH to Ethernet, which is a last resort. IP-RAN and PTN have now converged, and there is not much difference. They can be regarded as a comprehensive challenge to SDH, and now it seems to be a victory.

SDH, MSTP, WDM, PTN, OTN and ASON

SDH-based MSTP improves the traditional SDH. In addition to the functions of the standard SDH transmission node, it also has functions such as access and transmission of TDM services, ATM services and Ethernet services. The emergence of MSTP solves the requirement that traditional SDH technology cannot effectively handle data transmission. However, the core of MSTP is still circuit switching. In the face of ALL IP-based telecom services, although there is still a long living space, it will eventually be gradually replaced by PTN.

ASON is a new transmission network that integrates switching technology in transmission. The specific implementation is to introduce the control plane in addition to the transport plane and the management plane of the original transport network to form the interaction among the transport plane, the control plane and the management plane. Due to the introduction of the control plane into the ASON network structure, ASON has the following characteristics: Supporting fast service configuration; Supporting traffic engineering, allowing dynamic allocation of network resources; Adopting special control plane protocols, which can be applied to various transmission technologies; It has powerful protection function; realizes recovery function according to real-time transmission network status; supports connection control in multi-vendor environment; can introduce new supplementary services (such as closed user group and virtual private network); The operation of the technology supports the needs of the system software, etc.

Generally speaking, ASON has two main characteristics: First, the establishment, modification and deletion of connections are realized by users; the second is perfect network survival technology. GMPLS (General Multi-Protocol Label Switching), the key technology of the control plane of the optical network, is extended from MPLS. It extends the label and LSP (Label Switching Path) establishment mechanism of MPLS, resulting in a general label and general LSP ( GLSP). In addition to supporting interfaces with packet switching capabilities, GMPLS also supports interfaces with time division, space division, and wavelength switching capabilities. That is to say, the transport plane of ASON can be SDH, MSTP, WDM, OTN, and PTN. Therefore, simply speaking, MSTP can be used as a transport plane technology of ASON. In addition, in terms of network application level, MSTP is mostly used in metropolitan area networks, while ASON has a wider application range and a higher network level.

In terms of technological maturity, MSTP technology has been relatively complete and mature since 2004. Basically, after 2005, there will be no further breakthroughs in MSTP, and various manufacturers have turned to PTN for the transmission/bearer technology of metro areas. At present, only ASON based on SDH and OTN is relatively mature, and ASON based on ROADM and OBS is not yet mature. , there are still many problems to be solved in the interoperability between operators.

The traditional transmission network has only the transmission plane (inaccurately can be understood as transmission equipment) and management plane (inaccurately can be understood as network management). The biggest difference between ASON and the traditional transmission network is the introduction of the control plane (mainly the GMPLS protocol family). , including routing, signaling, control and other protocols) makes the transmission network have the intelligent characteristics of the previous data network: such as automatic discovery of network topology, intelligent realization of end-to-end service configuration, service SLA, network traffic balance, different protection levels The functions of mutual conversion of services and path restoration.

ASON has no special requirements on the technology of the transport plane itself. SDH, MSTP, DWDM, OTN, and PTN can all be used as the transport plane of ASON.

Therefore, non-transmission majors can approximate: ASON = transport network + control plane (GMPLS protocol). The transport network includes SDH, MSTP, DWDM, OTN, and PTN. To implement the ASON function, the network element can transplant the intelligent control software module on the traditional transmission equipment, and use the physical link channel provided by the equipment to complete the protocol intercommunication between the network elements. , the ASON network is implemented.

If the network composed of MSTP devices that support the ASON intelligent protocol does not use the intelligent protocol, it can be regarded as an MSTP network, and if the intelligent protocol is used, it is an ASON network.

The intelligent switching network whose transport plane is WDM or OTN is also called WSON.